Well, 60+ hours and a lot of frustration later, I beat Dark Souls.
When I was ready to give up on Kalameet I decided to revive on my last try. If I couldn't find anyone to co-op, I was fucked anyways so why not. Turns out someone was available. A guy who was naked and equipped with the dragon tooth.
So we went to Kalameet, and we finally killed the motherfucker. Sigh of relief. He even cut the tail for me, and I ended using the sword to kill Gwyn, but I'm heading ahead of myself. Thanks, overpowered stranger. I'm forever in your debt.
So, Gwyn. Took me about two hours. I'd say it was harder than Manus but easier than Kalameet. I still died a lot but at least I could kill him without help. There's a moment where the fight just clicks and you figure out his moves and the windows of opportunity to attack. Once I did (and it sure took me a long time), it only took a few tries.
I lit the final bonfire and the game kinda... ended? I'm guessing that I fulfilled the prophecy and took over as Gwyn's successor, etc., I expected the ending to be at least a bit more fleshed out. I know there's another ending, I'll probably youtube it later.
So, what can I say? I loved the game. I really liked Demon's but this was much better. This game is longer, has more variety, more bosses, and I loved the connected world. I know I missed tons of stuff and I'd like to go back to it at some point with a guide. I'm not one to replay games but I feel like there's so much I didn't do during this playthrough.